Yesterday I wrote about list in F#. Today I’ll write about arrays, which unlike lists are a mutable flat storage and cannot be resized. That means you have to create a new array if you want to remove or add elements. Advantages include constant look-up time and the fact that they can store a large amount of data.<\/p>\n
You can create a literal array in a similar way with the lists, placing the elements between [| |]:<\/p>\n
\r\nlet data1 = [|1;2;3;4|]\r\nprintfn \"data1: %a\" output_any data1\r\n<\/pre>\n\r\ndata1: [|1; 2; 3; 4|]\r\n<\/pre>\nThe empty literal array is [||].<\/p>\n
To create an array you can either use Array.create or Array.init. They both create and initialize an array, but the second makes a lambda expression, which allows advance initialization possibilities. The following creates an array with 10 elements initialized to 1:\n<\/p>\n
\r\nlet data2 = Array.create 10 1\r\nprintfn \"data2: %a\" output_any data2\r\n<\/pre>\nHere is the output:<\/p>\n
\r\ndata2: [|1; 1; 1; 1; 1; 1; 1; 1; 1; 1|]\r\n<\/pre>\nThe same can be achieved using Array.init:<\/p>\n
\r\nlet data3 = Array.init 10 (fun x -> 1)\r\nprintfn \"data3: %a\" output_any data3\r\n<\/pre>\n\r\ndata3: [|1; 1; 1; 1; 1; 1; 1; 1; 1; 1|]\r\n<\/pre>\nBut we can use Array.init to initialize the elements from 1 to N for instance:<\/p>\n
\r\nlet data4 = Array.init 10 (fun x -> x+1)\r\nprintfn \"data4: %a\" output_any data4\r\n<\/pre>\n\r\ndata4: [|1; 2; 3; 4; 5; 6; 7; 8; 9; 10|]\r\n<\/pre>\nThe arrays are mutable data structures. Elements are accessed with .[] or .(). The following code shows how to set the elements of an array:<\/p>\n
\r\nlet data5 = Array.create 10 0\r\nfor i = 0 to (Array.length data5)-1 do\r\n data5.[i] <- i+1\r\n\r\nprintfn \"data5: %a\" output_any data5\r\n<\/pre>\n\r\ndata5: [|1; 2; 3; 4; 5; 6; 7; 8; 9; 10|]\r\n<\/pre>\nYou can iterate over the elements of an array with Array.iter and Array.iteri, the second also providing access to the index of the elements.<\/p>\n
\r\ndata4 |> Array.iter (fun x -> printf \"%d \" x)\r\nprintfn \"\"\r\n \r\ndata4 |> Array.iteri (fun i x -> printfn \"data4(%d) = %d\" i x)\r\n<\/pre>\n\r\n1 2 3 4 5 6 7 8 9 10\r\ndata4(0) = 1\r\ndata4(1) = 2\r\ndata4(2) = 3\r\ndata4(3) = 4\r\ndata4(4) = 5\r\ndata4(5) = 6\r\ndata4(6) = 7\r\ndata4(7) = 8\r\ndata4(8) = 9\r\ndata4(9) = 10\r\n<\/pre>\nRetrieving the length of the array can either be done with Array.length arr or with arr.Length.<\/p>\n
\r\nfor i = 0 to data4.Length-1 do\r\n printfn \"data4(%d) = %d\" i data4.(i)\r\n<\/pre>\n\r\ndata4(0) = 1\r\ndata4(1) = 2\r\ndata4(2) = 3\r\ndata4(3) = 4\r\ndata4(4) = 5\r\ndata4(5) = 6\r\ndata4(6) = 7\r\ndata4(7) = 8\r\ndata4(8) = 9\r\ndata4(9) = 10\r\n<\/pre>\nLike the lists, arrays provide mapping that creates a new array by applying a function on all the elements of an array (with Array.map) or two arrays (with Array.map2).<\/p>\n
\r\nlet data6 = data4 |> Array.map (fun x -> x*2)\r\nprintfn \"data6: %a\" output_any data6\r\n \r\nlet data7 = Array.map2 (fun x y -> x+y) data4 data6\r\nprintfn \"data7: %a\" output_any data7\r\n<\/pre>\n\r\ndata6: [|2; 4; 6; 8; 10; 12; 14; 16; 18; 20|]\r\ndata7: [|3; 6; 9; 12; 15; 18; 21; 24; 27; 30|]\r\n<\/pre>\nA copy of an array can be done with Array.copy.<\/p>\n
\r\nlet data7 = Array.copy data6\r\nprintfn \"data7: %a\" output_any data7\r\n<\/pre>\n\r\ndata7: [|2; 4; 6; 8; 10; 12; 14; 16; 18; 20|]\r\n<\/pre>\nAppending elements to an array is also possible with Array.append, but the result is a new array, created by concatenating two arrays.<\/p>\n
\r\nlet data8 = Array.append data7 [|100|]\r\nprintfn \"data8: %a\" output_any data8\r\n<\/pre>\n\r\ndata8: [|2; 4; 6; 8; 10; 12; 14; 16; 18; 20; 100|]\r\n<\/pre>\nThe last operation of arrays I'm going to mention here is the folding, which allows applying a function to all the elements of an array, threading an accumulator argument in the process. The following example shows how to compute the sum of the elements of an array.\n<\/p>\n
\r\nlet data9 = [|1;2;3;4|]\r\nlet sum1 = (Array.fold_left (fun acc x-> x + acc) 0 data9)\r\nlet sum2 = (Array.fold_right (fun acc x-> x + acc) data9 0)\r\nprintfn \"sum1 = %d\" sum1\r\nprintfn \"sum2 = %d\" sum2\r\n<\/pre>\n\r\nsum1 = 10\r\nsum2 = 10\r\n<\/pre>\n<\/p>\n","protected":false},"excerpt":{"rendered":"
Yesterday I wrote about list in F#. Today I’ll write about arrays, which unlike lists are a mutable flat storage and cannot be resized. That means you have to create a new array if you want to remove or add elements. Advantages include constant look-up time and the fact that they can store a large … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[37,38],"tags":[],"class_list":["post-109","post","type-post","status-publish","format-standard","hentry","category-fsharp","category-tutorials"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t